The purpose is to determine whether intranasal administration of DDAVP 2 hours prior to infusion of very high purity (monoclonal antibody purified plasma-derived or recombinant) human FVIII concentrate in 10 patients with severe hemophilia A will prolong plasma half life of the infused FVIII. Prolonging the circulating half life of a FVIII concentrate would facilitate delivery of cost-effective inpatient and outpatient care to patients with hemophilia.